The overall objective of this project is to isolate overlapping clones representing the euchromatic part of the Drosophila genome. This will be accomplished in three steps. First, the euchromatic portions of the salivary gland chromosomes will be microdissected into regions of approximately 200-300 kb and the genomic DNA from each region cloned into a lambda bacteriophage vector. This will yield approximately 600 minilibraries representing part of the sequence complexity of each interval. Second, the unique sequence clones in each minilibrary will be used to screen an ordered and complete library, constructed in a cosmid vector designed for efficient use of the clones for subsequent chromosomal walking and/or P-factor mediated transformation experiments. The overlaps between cosmids from each microdissected region will be established by restriction mapping. For the majority of regions, it is likely that the overlapping cosmids will define a single continuous stretch of genomic DNA (a contig). In addition, many of the interval contigs representing adjacent microslices will be connected simply from the restriction maps. Third, given sufficient time, the remaining gaps will be closed by limited chromosomal walking between unconnected contigs. This project will advance substantially an understanding of the structural organization of the genome of this important model organism and contribute to the development of techniques important for characterizing more complex genomes. Furthermore, the clones obtained will be invaluable to many Drosophilists for studying specific genes and their environs.